Officials are probing how a 51-year-old highway bridge came to collapse in the Italian port city of Genoa yesterday, killing at least 26 people and injuring 16 others as it sent dozens of vehicles tumbling into a heap of concrete and twisted steel.

Australia's terror alert remains medium

Australia's terror alert will remain at medium despite the United Kingdom increasing its assessment of risk from substantial to severe, the second-highest level.

The alert level is regularly reviewed by authorities and would be increased to high "if it were deemed that a terrorist attack is likely to occur," Attorney-General George Brandis said in a statement on Saturday.

Senator Brandis said the government was seriously concerned that about 60 Australians were fighting in Syria and Iraq and another 100 believed to be involved.

"We remain in close contact with the United Kingdom and other partners about the threat from terrorist groups active in Syria and Iraq, and from returning foreign fighters," he said.

The UK's terror level was on Friday boosted to severe but Home Secretary Theresa May said there wasn't any specific threat.

"This move by the United Kingdom indicates the significance of the threat posed by the Islamic State and other terrorist groups in Syria and Iraq," Senator Brandis said.